Infinite heat control with quick heating



Oct. 21, 1969 c. c. GAMBll-L.

INFINITE HEAT CONTROL WITH QUICK BEATING 2 Sheets-Sheet 1 Filed Feb. 5, 1967 m Wm M m m &

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ATTORNEY Oct. 21, 1969 c, c, GAMB|LL 3,474,227

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f 5 BY mar/es C. (Fazzfizf/ 4444M ATTORNEY United States Patent 3,474,227 INFINITE HEAT CONTROL WITH QUICK HEATING Charles C. Gambill, Kokomo, Ind., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Feb. 3, 1967, Ser. No. 613,904 Int. Cl. Hb 3/6'8 US. Cl. 219-450 6 Claims ABSTRACT OF THE DISCLOSURE In the preferred form, a ferrite keeper with a low curie point is responsive to the temperature of a pan to be heated. Below the curie point, a permanent magnet is attracted to the keeper to close a switch which either directly or through a relay closes a shunt which shunts an infinite heat control and continuously connects the surface heater to the power source until the ferrite keeper is heated to its curie point and releases the permanent magnet to open the shunt switch and render effective the infinite heat control.

This invention pertains to an improved control providing rapid initial energization or heating of an electric heater such as a surface heater of an electric range prior to energization at a reduced average rate.

It has been customary to provide at least one surface heater of an electric range with an infinite heat control providing an infinite series of reduced heating rates. To provide quick initial heating there is added a flasher arrangement wherein there is initially applied a higher than normal voltage until the heater reaches a cherry red state. However, some of the advantages of the flasher arrangement are lost by an inherent time interval between the termination of the flasher heating and the supplying of the reduced energization under the infinite heat control. Also, if the flasher heating is not terminated when the heater reaches the cherry red state, the heater will be overheated and will be seriously damaged.

It is an object of this invention to provide a control with quick initial heating without exceeding a maximum safe rate and temperature, which after the quick initial heating will energize the heater at various desired selected average heating rates without any long interruptions.

This and other objects are attained in the forms shown in the drawings in which a permanent magnet is directly connected to a set of contacts which are moved to closed position when the permanent magnet has lifted substantially into contact with a ferrite keeper. The structure holding the ferrite keeper is spring pressed into engagement with any pan resting upon a surface heater surrounding it. As long as the ferrite keeper is at a temperature below its curie point the permanent magnet will be attracted to close the contacts which either through a bimetal relay or directly close a shunt which shunts the infinite heat control to continuously energize the surface heater at a maximum rate. When the pan is heated sufficiently to bring the ferrite keeper to a temperature above its curie point, the permanent magnet will release to open the associated contacts to place the surface heater under the control of the infinite heat control to thereafter supply heat at the desired average rate.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown.

In the drawings:

FIGURE 1 is a top view of a portion of an electric range illustrating a surface heater embodying one form of my invention;

FIGURE 2 is a vertical sectional view taken along the line 22 of FIGURE 1 illustrating the pan sensor;

FIGURE 3 is a wiring diagram showing one form of my invention;

FIGURE 4 is a modified wiring diagram showing a simplified form of my invention; and

FIGURE 5 is another modified wiring diagram showing another simplified form of my invention.

Referring now to the drawings and more particularly to FIGURES l and 2, there is illustrated the top surface 20 of an electric range with a surface heater 22 of the sheathed tubular type which extends in a generally spiral arrangement around the pan sensor control 24. The pan sensor control 24 includes an inverted cup-shaped metal member 26 of nonmagnetic stainless steel or aluminum provided with a cap 28 of aluminum which is pressed into an aperture in the center of the cup-shaped member 26 until its flange 30 rests on the top thereof. This cap member 28 contains on its underside a thin ferrite keeper disc 32 which is held by staked projections 34 extending from the cap member 28. Directly beneath the ferrite disc keeper 32 is a U-shaped permanent magnet 36 having riveted to it a member 38 provided with a threaded socket receiving a screw 40. The screw 40 threads through a disc shaped contact member 42 and fastens it to the member 38. The member 38 extends loosely through a central aperture in the insulating member 44 which carries a set of spaced contacts 46 and 48.

The ferrite disc keeper preferably is made of such a composition and made in such a way that it has a curie point at about 135 F. One example of such a ferrite as expressed in mol percentage is as follows:

Percent Fe O 46.1 NiO 9.8 ZnO 35.0 C0 0 .16 CuO 9.0

This ferrite disc keeper is made by powdering the ingredients, mixing and pressing the ingredients into the shape of a disc about one-half inch in diameter and onesixteenth of an inch thick. This disc is heated at a rate of 400 F. per hour to 2250 F. and held at that temperature of 2250 F. for one and one-half hours.

When this ferrite disc keeper 32 is below its curie point, the permanent magnet 36 will be attracted to lift the contact disc 42 into bridging engagement with the con tacts 46 and 48 to close the shunt circuit. The insulating member 44 is fastened to the inverted cup-shaped member 26 by a pair of Z-shaped brackets 50. The insulating member 44 is also fastened to the top of a pair of vertical guide members 52 which are mounted for vertical movement through apertures in the bottom support 54. The inverted cup member 26 and the cap member 28 are spring pressed upwardly by the long coil spring 56 supported at the bottom by the support 54 and extending upwardly to the brackets and inverted cap member 26. This spring as well as the switch and connections are enclosed in the cylindrical housing 58 of non-magnetic stainless steel which has its lower end fastened to and supported by the support 54.

As shown in FIGURE 3, one of the switch contacts 48 is connected by the conductor 60 to the heater 62 of a 'bimetal relay 64. The other contact 46 is connected by the conductor 66 to one terminal of the low voltage output winding of a transformer 68 while the other terminal of this output transformer winding is connected by the conductor 70 to the other terminal of the heater '62. The bimetal relay 64 includes a bimetal switch 72 which is adjusted by a cam 74. This switch closes upon heating and opens upon cooling. The cam 74 is also mechanically connected through a shaft 76 with a cam 78 adjusting the bimetal switch 80 of the infinite heat control which includes an electric heater 82 connected in series with the bimetal switch 80 and one terminal of the surface heater 22. The bimetal switch 72 is connected in shunt with the bimetal switch 80 and the heater 82 by the shunt circuit 84 having one of its terminals connected to the conductor 86 extending between the heater 82 and the heater 22 and the other of its terminals connected to the supply conductor 88 which also connects to the other terminal of the switch 80. The shaft 76 also extends to a cam 90 and an adjusting knob 92 which is rotated to throw the double pole switch 94, 96 to the open or closed position and also to select the heating rates desired for the infinite heat control 80, 82. The cam 74 is also simultaneously rotated to prevent the closing of the switch 72 at low rates of the infinite heat control 80, 82. The switch 96 connects the supply conductor 98 to the conductor 121 connecting with the second terminal of the surface heater 22. The switch 94 is connected by the conductor 123 to the conductor 98 and is connected by the conductor 125 to the branch conductor 127 connecting with one terminal of the input winding of the transformer 68. The conductor 125 also connects to the indicator lamp 129. The second terminal of the input winding of the transformer 68 as well as the second terminal of the lamp 129 are connected to the neutral supply conductor 131. The switches 80, 94 and 96 are enclosed in a single housing 133.

When a pan or other cooking vessel 135 is placed upon the surface heater 22 it will also contact the cap member 28 which normally projects above the surface heater 22. The spring permits the cam member 28 to retract to allow the pan to rest on the surface heater 22. The knob 92 is then turned to the desired final heating rate. The cams 74 and 78 will adjust the switches 72 and 80 to correspond to the desired average heating rate. The permanent magnet 36 remains attracted to its ferrite keeper 32 thereby keeping the bridging switch member 42 in contact with the cooperating switch contacts 46 and 48. This will energize the heater 62 to keep closed the bimetal switch 72 in all except the lower heating rate positions of the knob 92 and the earns 74 and '78. The surface heater 22 will then be continuously connected through the closed switches 96, 72 and 80 across the 236 volt supply conductors 88 and 98 to provide full wattage input thereto. The pan or vessel 135 will thereafter be heated at the maximum rate until the heat transmitted to the ferrite keeper disc 32 is sufficient to raise it above its curie point of about 135 F. The temperatures of the keeper disc 32 will lag behind the temperature of the pan or vessel 135 by about 30 to 50 F. depending upon the mass of the pan or vessel 135 and the contents thereof. The pan or vessel 135 will reach a temperature of 165 F. to 185 F. when the keeper disc 32 reaches the curie point.

When the ferrite keeper disc 32 is heated above its curie point, the permanent magnet 36 will release therefrom and drop to its open circuit position thereby moving the bridging contact 42 downwardly away from the contacts 46 and 48 to open the circuit of the heater 62. This will allow the bimetal switch 72 to cool and open thereby opening the shunt circuit 84 and rendering effective the infinite heat control 80, 82 which will thereafter control the heating rate of the heater 22 in accordance with the selected position of the knob 92 and the cam 78. This will continue until the surface heater 22 is shut off by the rotation of the knob 92 to open the switches 94 and 96. This deenergizes the system and extinguishes the lamp 129.,

In FIGURE 4 the circuit is identical and bears the same reference characters with the exception that the conductors 166 and 170 replace the conductors 66 and 70 of FIGURE 3 and are connected directly to the opposite terminals of the lamp 129. This eliminates the transformer 68 and places the contacts 42, 46 and 48 and the heater 62 under the same voltage as the lamp 129, namely 118 4 volts. The system illustrated in FIGURE 4 operates in the same manner as the system illustrated in FIGURE 3.

In the system shown in FIGURE 5 the bi-metal relay 64 is omitted and a switch 172 is placed directly in the shunt circuit which includes the contacts 42, 46 and 48 as well as the conductors 184, 185 and 1'87 which shunts the infinite heat control 80, 82. In this particular circuit, in all the low rate port-ions of the knob 92 and the shaft 76 up to a preselected low rate setting (such as 200 F. for example) the cam 174 keeps open the switch 172 to place in complete control the infinite heat control 80, 82 to energize the surface heater 22 at the low preselected average rate desired. This will bring foods or liquids requiring a low heating rate to their desired temperature more slowly to prevent scorching or burning or other undesirable results. At settings above the preselected low rate (such as 200 F.) the switch 172 will be closed by the cam 174 to initially shunt the infinite heat control 80, 82. Through this shunt the heater 82 is continuously energized at its maximum rate until the ferrite keeper disc 32 is heated sufliciently to bring it above its curie point F.) Since there is a lag between the vessel heated and the ferrite keeper disc 32 of about 50 F. this will mean that the surface heater 22 will be continuously energized until the vessel is heated to about F. The permanent magnet 36 then releases and opens the contacts 42, 46, 48 thereby opening the shunt around the infinite heater control 80, 82 to place the surface heater 22 thereafter continuously under the control of the infinite heat control 80, 82 to achieve the desired heating rate until the control is reset.

While the embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. In combination, an electric heater adapted to heat a body in heat transfer with it, an adjustable current control means connected in series with said electric heater including movable adjustment means for varying the average current flow to said heater from a very low rate to a high rate, a shunt circuit for shunting said current control means to obtain a higher rate of current flow to said heater than provided by said current control means when adjusted to any rate below its highest selected rate, said shunt circuit being provided with shunt circuit opening means, temperature responsive means adapted to be responsive to the temperature of the body to be heated having means effective below a predetermined temperature for closing said shunt circuit opening means for supplying current to said heater at a higher rate than the rate provided by said current control means and means operated by said movable adjustment means and effective only in the lower rates of adjustment for preventing the closing of said shunt circuit opening means only in lower rates of adjustment of said movable adjustment means.

2. A combination as defined in claim 1 in which the temperature responsive means comprises a temperature responsive magnetic material adapted to be responsive to the temperature of the body to be heated and having a curie point below 212 F. and a permanent magnet magnetically associated with said magnetic material, and means for mounting said permanent magnet and said magnetic material for movement relative to each other for controlling the closing and opening of said shunt circuit opening means.

3. A combination as defined in claim 1 in which said adjustment means comprises a movable shaft which is movable to adjust the control means from a very low rate to a high rate, said shaft means being provided with cam means effective only in the positions corresponding to the lower rates of adjustment for preventing the closing of said shunt circuit opening means.

4. A combination as defined in claim 1 in which the shunt circuit opening means includes a first switch operated to open position by said temperature responsive means above a predetermined temperature and a second switch operated by said movable adjustment means toopen position only in positions corresponding to the lower rates of adjustment.

5. In combination, an electric heater adapted to heat a body in heat transfer with it, an adjustable current control means connected in series with said electric heater including movable adjustment means for varying the average current flow to said heater from a very low rate to a high rate, a shunt circuit for shunting said current control means to obtain a higher rate of current flow through said heater than provided by said current control means when adjusted to any rate below its highest selected rate, said shunt circuit being provided with a normally open relay, temperature responsive means adapted to be responsive to the temperature of the body to be heated having means effective below a predetermined temperature for energizing said relay and eifective above said predetermined temperature for de-energizing said relay, and means operated by said movable adjustment means and effective only in positions corresponding to the lower rates of adjustment for preventing the closing of said relay.

-6. A combination as defined in claim 5 in which the temperature responsive means comprises a temperature responsive magnetic material having a curie point below 212 F. and a permanent magnet magnetically associated with said magnetic material, and means for mounting said permanent magnet and said magnetic material for relative movement toward each other for controlling the energization and de-energization of said relay.

References Cited UNITED STATES PATENTS 3,328,561 6/1967 SakamOto et al 219-450 3,118,044 1/1964 Holtkamp 219450 2,663,785 12/1953 Graham 2l9495 BERNARD A. GILHEANY, Primary Examiner 20 F. E. BELL, Assistant Examiner 

